The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a method for fabricating a semiconductor device including a ruthenium electrode.
As memory devices become more highly integrated due to the development of semiconductor process technology, a unit cell surface area of the memory devices is decreased and a driving voltage is lowered. In a capacitor including a silicon-insulator-silicon (SIS) structure, it is difficult to secure a capacitance of greater than approximately 25 fF due to the existence of an interfacial oxide layer. Thus, a capacitor including a metal-insulator-metal (MIM) cylinder structure using a metal electrode has been developed. Meanwhile, high-k materials, such as titanium oxide (TiO2), tantalum oxide (Ta2O5), and strontium titanate (SrTiO3), are expected to be used for a dielectric layer in a semiconductor memory device having the design rule of approximately 45 nm or less. It has been reported that a phase or a preferred orientation having a higher dielectric constant than that of a typical titanium nitride (TiN) electrode may be obtained when ruthenium (Ru) is used as an electrode material.
However, oxygen (O2) is typically used as a reaction gas when a ruthenium electrode is formed using a chemical vapor deposition (CVD) method or an atomic layer deposition (ALD) method. In such a case, a contact resistance (Rc) may increase due to the oxidation of a TiN diffusion barrier layer formed below the ruthenium electrode in an initial stage of deposition. Also, a regional lifting may occur after the deposition due to a deteriorated adhesion with an etch stop layer, including silicon nitride (Si3N4), which supports a bottom portion of the ruthenium electrode as shown in FIG. 1. Consequently, a bottom oxide layer may be wet etched during a full dip-out process while forming the capacitor having a cylinder or stack structure. Thus, a leaning of a bottom electrode may occur.
FIG. 1 illustrates a micrographic view showing a lifting occurred in a typical ruthenium electrode. The lifting is occurred on an interface between the ruthenium electrode and a titanium nitride (TiN) plug, or between the ruthenium electrode and the silicon nitride (Si3N4) layer. FIG. 2 illustrates a micrographic view showing leaning of storage nodes.